1. Field of the Invention
The present invention relates to processes for the extraction of crude oil from underground deposits.
2. Discussion of the Background
In the extraction of oil from source rock primary extraction processes generally only manage to raise a fraction of the oil originally present. In this case the oil reaches the earth's surface as a consequence of the natural pressure in the deposit. In secondary oil extraction, water is usually forced into one or more production wells in the formation and the oil is driven to one or more injection wells and then brought to the earth's surface.
This so-called water flooding as a secondary measure is relatively cheap and is used correspondingly frequently. But in many cases this method only leads to little additional oil extraction from the deposit.
Effective displacement of the oil, which is expensive but which is economically necessary in view of the future scarcity of oil, is achieved by tertiary measures. These are processes in which either the viscosity of the oil is lowered and/or the viscosity of water used for secondary flooding is raised and/or the interfacial tension between water and oil is lowered.
The majority of these processes can be classified as (1) dissolving or mixing flooding, (2) thermal oil extraction processes, (3) surfactant or polymer flooding or (4) as a combination of several of the processes mentioned.
Dissolving or mixing processes consist of injecting a solvent for the crude oil into the deposit. This solvent can be a gas and/or a liquid.
Thermal extraction processes include the injection of steam or hot water or they take place as underground combustion.
In the surfactant processes differentiation is made, depending on the surfactant concentration and possibly on the surfactant type and additives, between surfactant-assisted water flooding, micellar flooding and emulsion flooding. Surfactant-assisted water flooding is a process which, for example, can serve to increase the injection efficiency of injection wells or represents a "low-tension process." The action of the surfactant flooding is based primarily on a sharp reduction of the interfacial tension between oil and flooding water. The wettability of the rock surface and the mobility conditions are also of great importance. Favorable mobility conditions between oil and water are achieved by means of polymers.
These methods are not fully satisfactory however because they do not provide fully satisfactory results with varying levels of salinity in the deposits or with varying temperatures in the deposits.